Adhesive with multistage curing and the utilization thereof during the production of composite materials

ABSTRACT

The invention relates to an adhesive containing two components A and B, whereby component A comprises both a functional group which can be polymerized by means of irradiation with UV beams as well as at least one functional group which is able to react with a compound having at least one acidic hydrogen atom and component B comprises at least two functional groups which can be polymerized by means of irradiation with UV beams or with electron beams. The adhesive is suitable for the production of composite materials and exhibits a high flexibility with a good initial bonding.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.09/581,372, filed Aug. 10, 2000 now U.S. Pat. No. 6,482,869 which claimspriority under 35 U.S.C. § 371 of PCT International Application Ser. No.PCT/EP98/07752, filed Dec. 1, 1998 which claims priority to GermanApplication Ser. No. 197 54 926.8, filed Dec. 10, 1997.

BACKGROUND OF THE INVENTION

The invention relates to an adhesive comprising two components A and B,component A having at least two different functional groups andcomponent B having at least two similar functional groups.

The mechanical production of composite materials, especially compositefilms, is frequently conducted in the art by lamination usingsolvent-based adhesives. From a variety of standpoints, however, such aprocedure is disadvantageous.

When using solvent-based adhesives in lamination, for example, it isnecessary to evaporate considerable volumes of solvent during thelaminating process, involving high energy consumption. A furthernecessity, for the purpose of avoiding the emission of solvent vaporsinto the atmosphere, is extensive cleaning of the waste air producedduring evaporation of the solvent. In recent times, therefore, thetendency when producing composite materials has been more and moretoward using solventless systems rather than those containing solvent.

However, the renunciation of solvents impacts very adversely on theprocessability of an adhesive. Adhesives suitable for producingcomposite materials are intended first to have a suitable processingviscosity but, as far as possible, to release only small volumes ofvolatiles into the environment. A further requirement of such adhesivesis that directly after application to at least one of the materials tobe joined, and after joining thereof, they possess sufficiently goodinitial adhesion to prevent, as far as possible, the bonded materialsfrom moving relative to one another. Furthermore, however, an adhesivebond of this kind should also possess a sufficient degree of flexibilityto withstand the various tensile and extension stresses to which thecomposite material is generally exposed while still at the processingstage, and to do so without damage to the adhesive bond and withoutdamage to the bonded material.

With the prior art, conventional, solvent-free adhesives, therefore,there is generally a fundamental disadvantage in that the adhesionproperties of the adhesive following application are unsatisfactory,owing to the low viscosity, and, accordingly, the adhesive bond may notbe subjected to any stresses until it has finally cured, in order thatthe composite material maintains the form intended by adhesive bonding.This, however, necessitates long curing times, which frequently negatethe economy of composite materials produced using such adhesives.

One approach to avoiding the disadvantages described above was to use amultistage-curing adhesive system in the production of compositematerials. Adhesives were used which in a first stage were subjected toa rapid, first curing reaction by irradiation. The strength of theadhesive bond following this first curing reaction was said to be suchas to enable the bonded articles or materials to be handled withoutproblems. In a second curing stage, the adhesive then cured furtheruntil it had reached the desired ultimate strength.

DE-A 29 13 676 discloses a process for producing composite films bymeans of solvent-free adhesives. It describes a solvent-free adhesivewhich is liquid at room temperature and consists of oligomeric and/orpolymeric esters and/or ethers which contain both free isocyanate groupsand free (meth)acrylate groups in one molecule.

EP-B 0 564 483 relates to reactive contact adhesives, processes forpreparing them, and their use. The document describes urethane-basedcoating compositions which are polymerizable in two stages and which byvirtue of the presence of UV-polymerizable acrylate groups can be curedin a first curing stage to a material which has solidified but cannotyet be embossed or deformed in such a manner as to impart structure,after which, in a second, subsequent stage, irreversible solidificationtakes place. To reduce the viscosity, monofunctional acrylates are addedto the adhesive. Following irradiation, the adhesive described exhibitspressure tack; the intended use of the contact adhesive described issaid to be the adhesive bonding of wood and/or plastics parts at up toabout 70° C., preferably at room temperature.

In many cases, composite materials are subjected directly after theirproduction to further processing operations which demand a high degreeof flexibility from the composite material. The adhesive bond present inthe composite material must therefore possess sufficient flexibility topermit its further processing, without adverse effects owing to a lackof flexibility of the adhesive bond. For this purpose it is necessaryfor the adhesive bond to possess, initially, sufficient strength toprevent separation of the composite material into its originalconstituents, but not yet to be so strong that adverse effects owing toan excessively strong adhesive bond arise under tensile or flexuralstress.

The adhesives known from the prior art have the disadvantage that theyexhibit either excessively strong initial adhesion, which has adeleterious effect on the flexibility of the material, or elseinadequate ultimate strength, which may be disadvantageous for theservice properties of the composite material. Furthermore, the reactivediluents described in the prior art are frequently not fully reacted.This may lead to odor nuisance and even, if appropriate, to a healthrisk owing to migrateable compounds of low molecular mass (migrants).

SUMMARY OF THE INVENTION

The object of the present invention was therefore to provide an adhesivewhich is suitable for producing composite materials especially forproducing film composites, which after bonding still results insufficient flexibility of the adhesive bond and after complete curingleads to composite materials having excellent strength values in respectof the adhesive bond.

The object of the invention is achieved by means of an adhesive whichcomprises a polymer of low viscosity that contains bothirradiation-polymerizable functional groups and moisture-curingfunctional groups and a compound having a molecular weight of at leastabout 100 and at least two irradiation-polymerizable functional groups.

The invention provides an adhesive comprising two components A and B,

-   (a) component A being at least one polymer having a molecular weight    (M_(n)) of at least 800 that has at least one functional group    polymerizable by irradiation with UV light or with electron beams    and has at least one functional group capable of reacting with a    compound having at least one acidic hydrogen atom, and-   (b) component B being at least one compound having a molecular    weight (M_(n)) of from about 100 to about 8000 which has at least    two functional groups polymerizable by irradiation with UV light or    with electron beams.

In one preferred embodiment of the present invention the molecularweight (M_(n)) of the at least one compound used as component B whichhas at least two functional groups polymerizable by irradiation with UVlight or with electron beams is from about 100 to about 2000.

A polymerizable functional group is a group which is able to react byfree-radical, anionic or cationic addition polymerization,polycondensation or polyaddition with a suitable, further functionalgroup, with an increase in the molecular weight of the molecule whichcarries it. In the case of an increase in molecular weight byfree-radical addition polymerization, the functional group is, generallyand preferably an olefinically unsaturated double bond. In the case ofan increase in molecular weight by polycondensation the functional groupmay, for example, be an acid group or an alcohol group; in the case ofpolyaddition, examples of suitable functional groups are isocyanategroups or epoxide groups.

A functional group polymerizable by irradiation with UV light or withelectron beams is suitably, for example, a group having an olefinicallyunsaturated double bond. In the context of the present invention,preferred olefinically unsaturated double bonds are those as present,for example, in the derivatives of acrylic acid or of styrene.Particularly suitable derivatives, which are also preferred in thecontext of the present invention, are those of acrylic acid, examplesbeing the acrylates and the methacrylates.

In the subsequent course of the text, when reference is being made tothe properties of an adhesive, the term “curing” or the like as commonlyused in general by the skilled worker will be utilized fairly often. The“curing” of a composition comprising polymerizable compounds is based ingeneral on a polymerization reaction which is associated at least withan increase in the molecular weight of the compounds present in thecomposition. Normally, however, crosslinking reactions also take placeat the same time. The terms “curing” or the like therefore relate, inthe context of the following text, to polymerization reactions such asmay take place within individual components of the composition inconnection with which the term is used in each case; for example, theradiation-induced polymerization of a component which carries doublebonds. The terms likewise relate to polymerization reactions as may takeplace between different components of the particular composition inquestion; for example, the reaction of a component which carriesisocyanate groups with a component which carries OH groups. The termsfurther relate to polymerization reactions as may take place between acomponent of the composition in question and a component which entersthe composition owing to external influence; for example, the reactionbetween isocyanate groups and atmospheric moisture.

In the context of the present invention, a functional group capable ofreacting with a compound having at least one acidic hydrogen atom is inparticular the isocyanate group or the epoxide group, the isocyanategroup being particularly preferred.

A compound having an acidic hydrogen atom is a compound having an activehydrogen atom which can be determined in accordance with the Zerevitinovtest and is attached to an N, O or S atom. This definition includes inparticular the hydrogen atoms of water and of carboxyl, amino, imino,hydroxyl, and thiol groups. In the context of the present invention,particular preference is given to water, or to compounds having aminogroups or hydroxyl groups or both, or to mixtures of two or morethereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Component A in the adhesive of the invention is at least one polymerhaving a molecular weight of at least 800. Polymers suitable for use ascomponent A are all polymeric compounds which may commonly be used inadhesives, examples being polyacrylates, polyesters, polyethers,polycarbonates, polyacetals, polyurethanes, polyolefins, or rubberpolymers such as nitrile rubber or styrene/butadiene rubber, providedthey have at least one functional group polymerizable by irradiationwith UV light or with electron beams and with at least one functionalgroup capable of reacting with a compound having at least one acidichydrogen atom.

In the adhesives of the invention it is preferred, however, to make useas component A of polyacrylates, polyesters or polyurethanes, sincethese polymers offer a particularly simple opportunity to attach thefunctional groups required by the invention to the polymer molecule.

The polymers which may be employed in accordance with the invention ascomponent A can be prepared with particular simplicity by starting froma base polymer which has in the polymer molecule at least two functionalgroups which are reactive with isocyanate groups, these groups beingpreferably OH groups. The desired functional group can be attached to abase polymer of this kind with particular simplicity by reaction with apolyisocyanate or with a suitably functionalized monoisocyanate.

A polymer suitable for use as the base polymer is, for example, apolymer selected from a group containing polyesters, polyethers,polycarbonates or polyacetals having a molecular weight (M_(n)) of atleast about 200, or mixtures of two or more thereof, which have terminalOH groups.

In the context of the present invention, polyesters which can be used asbase polymers for preparing component A may be obtained, in a mannerknown to the skilled worker, by polycondensation of acid components andalcohol components, in particular by polycondensation of apolycarboxylic acid or of a mixture of two or more polycarboxylic acidsand a polyol or a mixture of two or more polyols.

Polycarboxylic acids suitable in the context of the present inventionfor preparing the base polymer may have an aliphatic, cycloaliphatic,arylaliphatic, aromatic or heterocyclic parent structure and in additionto the at least two carboxylic acid groups may further comprise one ormore substituents which are nonreactive in a polycondensation, examplesbeing halogen atoms or olefinically unsaturated double bonds. Ifdesired, instead of the free carboxylic acids, it is also possible touse their anhydrides (where they exist) or their esters with C₁₋₅monoalcohols, or mixtures of two or more thereof, for thepolycondensation.

Examples of suitable polycarboxylic acids are succinic acid, adipicacid, suberic acid, azelaic acid, sebacic acid, glutaric acid, phthalicacid, isophthalic acid, terephthalic acid, trimellitic acid, phthalicanhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride,tetrachlorophthalic anhydride, endomethylenetetrahydrophthalicanhydride, glutaric anhydride, maleic acid, maleic anhydride, fumaricacid, dimeric fatty acids or trimeric fatty acids or mixtures of two ormore thereof. If desired, minor amounts of monofunctional fatty acidsmay be present in the reaction mixture.

As diols for preparing a polyester or polycarbonate which can be used asthe base polymer it is possible to use a large number of polyols.Examples are aliphatic polyols having from 2 to 4 OH groups permolecule. The OH groups may be an either primary or secondaryattachment. Examples of suitable aliphatic polyols include ethyleneglycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol,1,3-butanediol, 2,3-butanediol, 1,4-butenediol, 1,4-butanediol,1,5-pentanediol, and the isomeric pentanediols, pentanediols orpentanediols or mixtures of two or more thereof, 1,6-hexanediol, and theisomeric hexanediols, hexenediols or hexanediols or mixtures of two ormore thereof, 1,7-heptanediol and the isomeric heptane-, heptene- orheptanediol, 1,8-octanediol and the isomeric octane-, octene- oroctanediol, and the higher homologs or isomers of said compounds, asthey result for the skilled worker from a stepwise extension of thecarbon chain by one CH₂ group in each case or with introduction ofbranching into the carbon chain, or mixtures of two or more thereof.

Likewise suitable are alcohols of higher functionality, such asglycerol, trimethylolpropane, pentaerythritol or sugar alcohols such assorbitol or glucose, for example, and also oligomeric ethers of saidsubstances with themselves or in a mixture of two or more of saidcompounds with one another, an example being polyglycerol having adegree of polymerization of from about 2 to about 4. With the higherpolyfunctional alcohols it is also possible for one or more OH groups tobe esterified with monofunctional carboxylic acids having 1 to about 20carbon atoms, with the proviso that on average at least two OH groupsare retained. Said higher polyfunctional alcohols may be used in pureform or, where possible, as technical-grade mixtures obtainable in thesynthesis of said alcohols.

As the polyol component for preparing the base polymers a furtherpossibility is to use the reaction products of low molecular masspolyfunctional alcohols with alkylene oxides, which are known aspolyether polyols. Polyether polyols intended for use to preparepolyesters suitable as base polymers are preferably obtained by reactingpolyols with alkylene oxides. The alkylene oxides have preferably two toabout four carbon atoms. Suitable examples are the reaction products ofethylene glycol, propylene glycol, the isomeric butanediols orhexanediols as mentioned above, or mixtures of two or more thereof withethylene oxide, propylene oxide or butylene oxide or mixtures of two ormore thereof. Also suitable, furthermore, are the reaction products ofpolyfunctional alcohols such as glycerol, trimethylolethane ortrimethylolpropane, pentaerythritol or sugar alcohols or mixtures of twoor more thereof with said alkylene oxides to give polyether polyols.Particularly suitable polyether polyols are those obtainable from saidreactions and having a molecular weight (M_(n)) of from about 100 toabout 3000, preferably from about 200 to about 2000. Said polyetherpolyols may be reacted with the abovementioned polycarboxylic acids in apolycondensation reaction to give the polyesters which can be used asbase polymers.

Likewise suitable as base polymers having terminal OH groups arepolyether polyols, as produced, for example, in the manner depictedabove. Polyether polyols are normally obtained by reacting a startingcompound having at least two reactive hydrogen atoms with alkyleneoxides or arylene oxides, examples being ethylene oxide, propyleneoxide, butylene oxide, styrene oxide, tetrahydrofuran or epichlorohydrinor mixtures of two or more thereof.

Examples of suitable starting compounds are water, ethylene glycol, 1,2-or 1,3-propylene glycol, 1,4- or 1,3-butylene glycol, 1,6-hexanediol,1,8-octanediol, neopentyl glycol, 1,4-hydroxy-methylcyclohexane,2-methyl-1,3-propanediol, glycerol, trimethylolpropane,1,2,6-hexanetriol, 1,2,4-butane-triol, trimethylolethane,pentaerythritol, mannitol, sorbitol, methyl glactoside, sugars, phenol,isononylphenol, resorcinol, hydroquinone, 1,2,2- or 1,1,2-tris(hydroxyphenyl) ethane, ammonia, methylamine, ethylenediamine, tetra- orhexamethyleneamine, triethanolamine, aniline, phenylenediamine, 2,4- and2,6-diaminotoluene and polyphenylpolymethylene-polyamines as obtainableby aniline-formaldehyde condensation.

Likewise suitable for use as base component are polyether polyols whichhave been modified by vinyl polymers. Products of this kind areobtainable, for example, by polymerizing styrene or acrylonitrile or amixture thereof in the presence of polyethers.

A polyether polyol which is particularly suitable for use as a basepolymer in the context of the present invention is polypropylene glycolhaving a molecular weight from about 300 to about 1500.

Likewise suitable as the base polymer or as a polyol component forpreparing the base polymer are polyacetals. Polyacetals are compoundsobtainable by reacting glycols, such as diethylene glycol or hexanediol,for example, with formaldehyde. Polyacetals which can be used in thecontext of the invention may also be obtained by the polymerization ofcyclic acetals.

Further compounds suitable as base polymers or as polyols for preparingthe base polymers are polycarbonates. Polycarbonates may be obtained,for example, by the reaction of the abovementioned polyols, especiallyof diols such as propylene glycol, 1,4-butanediol or 1,6-hexanediol,diethylene glycol, triethylene glycol, tetraethylene glycol or mixturesof two or more thereof, with diaryl carbonates, an example beingdiphenyl carbonate or phosgene.

Likewise suitable as base polymers or as a polyol component forpreparing the base polymers are polyacrylates which carry OH groups.Such polyacrylates are obtainable, for example, by polymerizingethylenically unsaturated monomers which carry OH groups. Monomers ofthis kind are obtainable, for example, by esterifying ethylenicallyunsaturated carboxylic acids and difunctional alcohols, the alcoholgenerally being present only in a slight excess. Examples ofethylenically unsaturated carboxylic acids suitable for this purpose areacrylic acid, methacrylic acid, crotonic acid or maleic acid.Appropriate esters which carry OH groups are, for example,2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropylacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate or3-hydroxypropyl methacrylate or mixtures of two or more thereof.

It may be the case that the molecular weight of the base polymer is toolow for use as component A. An increase in the molecular weight can beaccomplished, for example, by chain extension. Advantageously, for thispurpose, the base polymer which carries terminal OH groups is firstreacted with a compound which is polyfunctional, preferablydifunctional, in respect of the terminal OH groups.

Suitable polyfunctional compounds in the sense of the invention aretherefore, in particular, polyepoxides, especially diepoxides, or,preferably, polyisocyanates, especially diisocyanates. Particularpreference is given in the context of the present invention to thediisocyanates. The stoichiometric proportions between base polymer andpolyfunctional compound that are required in order to achieve a definedincrease in molecular weight are known to the skilled worker. Ingeneral, however, it will be the case that in order to achieve a chainextension an excess of base polymer is present in the chain extensionreaction, with the resultant, chain-extended base polymers again havingterminal OH groups.

In order to be suitable for use as component A the abovementioned basepolymers which have terminal OH groups and may have been chain extendedmust be provided with at least one functional group polymerizable byirradiation with UV light or with electron beams and at least onefunctional group polymerizable by reaction with a compound having atleast one acidic hydrogen atom.

For this purpose, the base polymers are judiciously reacted with acompound which is polyfunctional, preferably difunctional, in respect ofthe terminal OH groups. Suitable polyfunctional compounds in the senseof the invention are the polyfunctional compounds which may already havebeen used for chain extension, especially polyepoxides, in particulardiepoxides, but preferably polyisocyanates, especially diisocyanates.Particular preference is given in the context of the present inventionto the diisocyanates.

Suitable polyfunctional polyisocyanates for reaction with the basepolymers contain on average from two to not more than about fourisocyanate groups. Examples of suitable isocyanates are 1,5-naphthalenediisocyanate, 4,4′-diphenylmethane diisocyanate (MDI), hydrogenated MDI(dicyclohexylmethane diisocyanate, H₁₂-MDI), xylylene diisocyanate(XDI), tetramethyl-xylylene diisocyanate (TMXDI),4,4′-diphenyl-dimethylmethane diisocyanate, and also di- andtetraalkyldiphenylmethane diisocyanate, 4,4′-bibenzyl diisocyanate,1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2,4- and2,6-tolylene diisocyanate (TDI) and mixtures thereof, especially amixture containing about 20% 2,4- and 80% by weight 2,6-tolylenediisocyanate, 1-methyl-2,4-diisocyanatocyclohexane,1,6-diisocyanato-2,2,4-trimethylhexane,1,6-diisocyanato-2,4,4-trimethylhexane,1-isocyanatomethyl-3-isocyanato-1,5,5-trimethylcyclohexane (IPDI),chlorinated and brominated diisocyanates, phosphorus-containingdiisocyanates, 4,4′-diisocyanatophenyl-perfluoroethane,tetramethoxybutane 1,4-diisocyanate, butane 1,4-diisocyanate, hexane1,6-diisocyanate (HDI), cyclohexane 1,4-diisocyanate, ethylenediisocyanate, bisisocyanatoethyl phthalate; polyisocyanates containingreactive halogen atoms, such as 1-chloromethylphenyl 2,4-diisocyanate,1-bromoethylphenyl 2,6-diisocyanate, and 3,3-bischloromethyl ether4,4′-diphenyldiisocyanate. It is also possible to use sulfur-containingpolyisocyanates, as obtainable, for example, by reacting 2 mol ofhexamethylene diisocyanate with 1 mol of thiodiglycol ordihydroxydihexyl sulfide. Other diisocyanates are trimethylhexamethylenediisocyanates, 1,4-diisocyanatobutane, 1,2-diisocyanatododecane, anddimeric fatty acid diisocyanates. Triisocyanato isocyanurates can beobtained by trimerizing diisocyanates at elevated temperatures, forexample, at about 200° and/or in the presence of a catalyst, forexample, an amine, and may likewise be used in the context of thepresent invention. In the context of the present invention saidpolyisocyanates may be used individually or as a mixture of two or moreof said polyisocyanates. Preferably, an individual polyisocyanate or amixture of two or three polyisocyanates is used in the context of thepresent invention. Preferred polyisocyanates for use individually or ina mixture are HDI, MDI or TDI; for example, a mixture of MDI and TDI.

The base polymer is reacted with the polyfunctional compound, preferablywith the diisocyanate, preferably in a ratio of 1:>2, the excess ofpolyfunctional compound being chosen, for example, to be just sufficientthat chain extension of the base polymer is avoided but only smallamounts of unreacted polyfunctional compound are present in component A.A procedure of this kind may be advantageous especially when using adiisocyanate as polyfunctional compound. In this way a polymer isobtained which carries, terminally, two functional groups polymerizableby reaction with a compound having at least one acidic hydrogen atom.

From a polymer of this kind, in order to obtain a polymer suitable foruse as component A, the polymer is reacted judiciously with a compoundhaving both a functional group polymerizable by irradiation with UVlight or with electron beams and a functional group suitable forreaction with the terminal functional group on the polymer. Particularlysuitable for this purpose are the hydroxyalkyl acrylates ormethacrylates, i.e., reaction products of acrylic acid or methacrylicacid with difunctional alcohols. Particularly suitable in the context ofthe present invention are, for example, 2-hydroxyethyl acrylate,2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropylmethacrylate, 3-hydroxypropyl acrylate or 3-hydroxypropyl methacrylate,or mixtures of two or more thereof.

The molar ratios between base polymer and the compound having both afunctional group polymerizable by irradiation with UV light or withelectron beams and a functional group capable of reacting with theterminal functional group on the polymer may vary within wide limits inthe reaction. In general it is the case that a higher proportion offunctional groups polymerizable by irradiation with UV light or withelectron beams in component A results in an increased strength of anadhesive bond, whereas a higher proportion of functional groups reactivewith a compound having at least one acidic hydrogen atom leads to ahigher ultimate strength.

If, for example, the base polymer is reacted in a molar ratio ofapproximately 1:1 with the compound which has both a functional grouppolymerizable by irradiation with UV light or with electron beams and afunctional group capable of reacting with the terminal functional groupon the polymer, then each polymer molecule in the polymer mixtureobtainable therefrom carries on average both one functional grouppolymerizable by irradiation with UV light or with electron beams andone functional group reactive with a compound having at least one acidichydrogen atom. Accordingly, the proportions of the two types offunctional groups in the polymer mixture obtainable by a reaction ofthis kind may be varied in each case between greater than 0 and lessthan 100% (based on functional groups in the sense of the presentinvention). Good results can be obtained, for example, if from about 1to about 50% of the functional groups present as terminal groups in thepolymer are functional groups polymerizable by irradiation with UV lightor with electron beams, preferably from about 5 to about 30%, and withparticular preference from about 8 to about 15%.

Polymers suitable for use in component A may, for example, also beobtained in a plurality of steps such that in a first step the basepolymer which carries terminal OH groups is reacted with a compoundwhich has both a functional group polymerizable by irradiation with UVlight or with electron beams and a functional group capable of reactingwith the terminal OH group on the base polymer. An example of such acompound is styrene isocyanate. Further such compounds may be obtained,for example, by reacting an approximately equimolar amount of ahydroxyalkyl acrylate or methacrylate with a diisocyanate. Followingreaction of an approximately equimolar amount of the base polymer (whichmay have been adapted by chain extension to the molecular weightrequired for use in component A) with such a compound a polymer isformed in a second step, which, terminally, has both an OH group and afunctional group polymerizable by irradiation with UV light or withelectron beams. If this polymer is reacted, for example, with adiisocyanate, the result is a polymer suitable for use in component A.

It is likewise possible to combine the two abovementioned steps byreacting in an appropriate molar ratio a base polymer, a diisocyanate(or, if desired, another polyfunctional compound in the abovementionedsense) and a compound having both a functional group polymerizable byirradiation with UV light or with electron beams and a functional groupcapable of reacting with the terminal OH group on the base polymer withone another so that the proportions of the two types of functionalgroups in the polymer mixture obtainable by such a reaction vary in eachcase between greater than 0% and less than 100% (based on functionalgroups). Good results can be obtained, for example, if from about 1 toabout 50% of the functional groups present as terminal groups in thepolymer are functional groups polymerizable by irradiation with UV lightor with electron beams, preferably from about 5 to about 30%, and withparticular preference from about 8 to about 15%.

At processing temperatures suitable for typical applications, typicalpolymers suitable for use in component A have a viscosity of from about1000 mPas to about 10,000 mPas, in particular from about 3000 mPas toabout 7000 mPas (Brookfield CAP 2000, 25-150° C., cone 6, 50 rpm,measurement time 25 s). Typical processing temperatures are, forexample, from about 25 to about 70° C. for the production of flexiblepackaging films, from about 70 to about 80° C. for the lamination ofhigh-gloss films, and from about 80 to about 150° C. for applications inthe textile sector.

Typical NCO values for polymers suitable for use in component A are fromabout 2.5% by weight to about 7% by weight, in particular from about3.5% by weight to about 5% by weight.

The component A used in the context of the present invention may consistonly of one of the polymers described; however, it may advantageouslyconstitute a mixture of two or more of said polymers. Thus it isadvantageous, for example, if the base polymer used comprises a mixtureof one or more polyester polyols and one or more polyether polyols. Thedifferent base polymers in this case may differ, for example, in themolecular weight (M_(n)) or in the chemical structure, or in bothrespects.

In one preferred embodiment of the invention the base polymers used toprepare component A comprise from about 20 to about 40% by weight ofpolyester polyols and from about 20 to about 60% by weight of polyetherpolyols, based on the total component A. In another preferred embodimentat least two different polyether polyols are used as base polymers inaddition to a polyester polyol; in particular, a mixture of onepolyether polyol having a molecular weight of from about 800 to about1500 and one polyether polyol having a molecular weight of from about300 to about 700.

To prepare component A it is possible, as described above, for theindividual base polymers to be equipped with functional groups and, ifdesired, chain extended so that they are suitable directly for use ascomponent A. In one preferred embodiment of the invention, however, amixture of OH-carrying base polymers is reacted first with anappropriate amount of polyisocyanates and subsequently, in anappropriate molar ratio, with compounds having both a functional grouppolymerizable by irradiation with UV light or with electron beams and afunctional group capable of reacting with the terminal OH group on thebase polymer.

As component B, the adhesives of the invention comprise at least onecompound having a molecular weight of from about 100 to about 8000 whichhas at least two functional groups polymerizable by irradiation with UVlight or with electron beams. Particularly suitable components B aredifunctional or higher polyfunctional acrylate or methacrylate esters.Such acrylate or methacrylate esters include, for example, esters ofacrylic acid or methacrylic acid with aromatic, aliphatic orcycloaliphatic polyols or acrylate esters of polyether alcohols.

Polyols which can be used to prepare an acrylate or methacrylate esterwhich can be used as component B may be a large number of polyols.Examples are aliphatic polyols having 2-4 OH groups per molecule and 2to about 40 carbon atoms. The OH groups may be in either primary orsecondary attachment. Suitable -aliphatic polyols include for exampleethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol,1,3-butanediol, 2,3-butanediol, 1,4-butenediol, 1,4-butanediol,1,5-pentanediol, and the isomeric pentanediols, pentanediols orpentanediols or mixtures of two or more thereof, 1,6-hexanediol, and theisomeric hexanediols, hexenediols or hexanediols or mixtures of two ormore thereof, 1,7-heptanediol and the isomeric heptane-, heptene- orheptanediol, 1,8-octanediol and the isomeric octane-, octene- oroctanediol, and the higher homologs or isomers of said compounds, asthey result for the skilled worker from a stepwise extension of thecarbon chain by one CH₂ group in each case or with introduction ofbranching into the carbon chain, or mixtures of two or more thereof.

Likewise suitable are alcohols of higher functionality, such asglycerol, trimethylolpropane, pentaerythritol or sugar alcohols such assorbitol or glucose, for example, and also oligomeric ethers of saidsubstances with themselves or in a mixture of two or more of saidcompounds with one another, an example being polyglycerol having adegree of polymerization of from about 2 to about 4. With thehigher-functional alcohols it is possible for one or more OH groups tobe esterified with monofunctional carboxylic acids having 1 to about 20carbon atoms, with the proviso that on average at least two OH groupsare retained. Said higher-functional alcohols may be used in pure formor, where possible, as technical-grade mixtures obtainable in thesynthesis of said alcohols.

As the polyol component for preparing the acrylate or methacrylateesters a further possibility is to use the reaction products of lowmolecular mass polyfunctional alcohols with alkylene oxides, which areknown as polyether polyols. Polyether polyols intended for use toprepare polyesters suitable as base polymers are preferably obtained byreacting polyols with alkylene oxides. The alkylene oxides havepreferably two to about four carbon atoms. Suitable examples are thereaction products of ethylene glycol, propylene glycol, the isomericbutanediols or hexanediols, as mentioned above, or mixtures of two ormore thereof, with ethylene oxide, propylene oxide or butylene oxide ormixtures of two or more thereof. Also suitable, furthermore, are thereaction products of polyfunctional alcohols such as glycerol,trimethylolethane or trimethylolpropane, pentaerythritol or sugaralcohols or mixtures of two or more thereof with said alkylene oxides togive polyether polyols. Particularly suitable polyether polyols arethose obtainable from said reactions and having a molecular weight(M_(n)) of from about 100 to about 2000, preferably from about 150 toabout 1500, in particular from about 150 to about 800.

Acrylate esters of aliphatic diols having 2 to about 40 carbon atomsinclude, for example, neopentyl glycol di(meth)acrylate, 1,6-hexanedioldi(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritoltetra(meth)acrylate, and (meth)acrylate esters of sorbitol and of othersugar alcohols. These (meth)acrylate esters of aliphatic orcycloaliphatic diols may be modified with an aliphatic ester or with analkylene oxide. The acrylates modified by an aliphatic ester include,for example, neopentyl glycol hydroxypivalate di(meth)acrylate,caprolactone-modified neopentyl glycol hydroxypivalate di(meth)acrylatesand the like. The alkylene oxide-modified acrylate compounds include,for example, ethylene oxide-modified neopentyl glycol di(meth)acrylates,propylene oxide-modified neopentyl glycol di(meth)acrylates, ethyleneoxide-modified 1,6-hexanediol di(meth)acrylates or propyleneoxide-modified 1,6-hexanediol di(meth)acrylates, or mixtures of two ormore thereof.

Acrylate monomers constructed on the basis of polyether polyols include,for example, neopentyl glycol-modified trimethylolpropanedi(meth)acrylates, polyethylene glycol di(meth)acrylates, polypropyleneglycol di(meth)acrylates and the like. Trifunctional and higherpolyfunctional acrylate monomers include, for example,trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate,dipentaerythritol tetra(meth)acrylate, dipentaerythritolpenta(meth)acrylate, dipentaerythritol hexa (meth)acrylate,caprolactone-modified dipentaerythritol hexa(meth)acrylate,pentaerythritol tetra(meth)acrylate, tris[(meth)acryloxyethyl]isocyanurate, caprolactone-modified tris[(meth)acryloxyethyl]isocyanurates or trimethylolpropane tetra(meth)acrylate, or mixtures oftwo or more thereof.

Among the abovementioned difunctional, trifunctional or higherpolyfunctional acrylate monomers which can be used in accordance withthe invention as component B, preference is given to tripropylene glycoldiacrylate, neopentyl glycol propoxylate di(meth)acrylate,trimethylolpropane tri (meth) acrylate, and pentaerythritol triacrylate.

The adhesives of the invention comprise component A in an amount of fromabout 10 to about 99.9% by weight, preferably from about 15 to about 99%by weight, and component B in an amount of from about 90 to about 0.1%by weight, preferably from about 85 to about 1% by weight, based on thesum of the components A and B.

In addition to component A and component B the adhesive may comprise ascomponent C at least one photoinitiator which under UV irradiationinitiates the polymerization of olefinically unsaturated double bonds.

As component C a photoinitiator is generally used, therefore, which onirradiation with light having a wavelength of from about 260 to about480 nm is able to initiate a free-radical polymerization of olefinicallyunsaturated double bonds. Suitable for use as component C in the contextof the present invention are, in principle, all customaryphotoinitiators that are compatible with the adhesive of the invention,i.e., which result in at least substantially homogeneous mixtures.

Examples of these are all Norrish type I fragmenting substances.Examples of such substances are benzophenone, camphorquinone, Quantacure(manufacturer: International Bio-Synthetics), Kayacure MBP(manufacturer: Nippon Kayaku), Esacure BO (manufacturer: FarrellLambert), Trigonal 14 (manufacturer: Akzo), photoinitiators of theIgacure®, Darocure® or Speedcure® series (manufacturer: Ciba-Geigy),Darocure® 1173 and/or Fi-4 (manufacturer: Eastman). Of these, particularsuitability is possessed by Irgacure® 651, Irgacure® 369, Irgacure® 184,Irgacure® 907, Irgacure® 1850, Irgacure® 1173 (Darocure® 1173),Irgacure® 1116, Speedcure® EDB, Speedcure® ITX, Irgacure® 784 orIrgacure® 2959, or mixtures of two or more thereof. Also suitable is2,4,6-trimethyl-benzenediphenylphosphine oxide (Lucirin TPO,manufacturer: BASF AG), which may also be used in a mixture of one ormore of the abovementioned photoinitiators.

Conventional photoinitiators of low molecular mass may contribute to theformation of migrants in composite materials. The migrants in questionare the photoinitiators themselves that are present in the adhesive; afurther source of migrants is constituted, however, by fragments of thephotoinitiators, as may be produced on irradiation of the adhesive withUV rays. Under certain circumstances—for example, when producingcomposite materials intended for use as food packaging—the presence ofmigrateable compounds in the adhesive is avoided as far as possible. Themigrateable compounds content of the adhesive of the invention cangenerally be reduced still further if the photoinitiator has a molecularweight which substantially hinders, or even prevents, migration.

In the context of a preferred embodiment, component C thereforecomprises, at least proportionally, a photoinitiator having a molecularweight of more than about 200. Commercially available photoinitiatorswhich meet this condition are, for example, Irgacure® 651, Irgacure®369, Irgacure® 907, Irgacure® 784, Speedcure® EDB, or Speedcure® ITX.

Photoinitiators which in terms of their molecular weight meet theabovementioned condition are also obtainable, however, by reacting a lowmolecular mass photoinitiator which has an isocyanate-reactivefunctional group—for example, an amino group or an OH group—with a highmolecular mass compound having at least one isocyanate group(polymer-bonded photoinitiators). As the component it is preferred touse compounds which carry more than one photoinitiator molecule—forexample, two, three or more photoinitiator molecules. Such compounds maybe obtained, for example, by reacting a polyfunctional alcohol havingtwo or more OH groups with suitable di- or triisocyanates andphotoinitiators having a suitable, isocyanate-reactive functional group.

Polyfunctional alcohols which can be used are all of the abovementionedpolyfunctional alcohols, but especially neopentyl glycol, glycerol,trimethylolpropane, pentaerythritol and alkoxylation products thereofwith C₂₋₄ alkylene oxides. Likewise suitable as polyfunctional alcohols,and particularly preferred in the context of the present invention, arethe reaction products of trihydric alcohols with caprolactone; forexample, the reaction product of trimethylolpropane with caprolactone(Capa ®305, from Interox, Cheshire, UK, molecular weight (M_(n))=540).

In one preferred embodiment of the invention, component C comprises aphotoinitiator obtainable by reacting an at least trihydric alcohol withcaprolactone to give a polycaprolactone which carries at least three OHgroups and has a molecular weight of from about 300 to about 900, andsubsequently linking the polycaprolactone with1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methylpropan-1-one by meansof a compound which carries at least two isocyanate groups.

As compounds which carry at least two isocyanate groups, especially asdiisocyanates for reaction with said polyols, suitable compoundsinclude, for example, all those diisocyanates specified within thistext. Particular preference is given, however, to the 2,4 and the 2,6isomer of tolylene diisocyanate (TDI), it being possible to use theisomers in their pure form or as a mixture.

Suitable photoinitiators for preparing the polymer-bondedphotoinitiators are all photoinitiators which have a functional groupwhich is reactive toward isocyanate groups. Particular preference isgiven in the context of the present invention to1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methylpropan-1-one (Irgacure®2959), which has an OH group in primary attachment.

If desired, the photoinitiators which can be used in component C mayalso be prepared by using a minor amount of photoinitiator moleculeswhich are reactive toward isocyanate groups when preparing component Aor component B or in both preparation processes. This leads to theattachment of the photoinitiator to a molecule of component A or ofcomponent B.

A further possibility is to effect the attachment of the photoinitiatorto a polymer chain, for example, to component A, by adding thephotoinitiator which has an appropriate functional group in monomericform to the adhesive and then, during a storage period of the adhesive,for instance, reacting it with a corresponding polymeric component, forexample, component A.

A further possibility is to provide the photoinitiator with a functionalgroup polymerizable by irradiation with UV light or with electron beams,the functional group polymerizable with UV light or with electron beamsbeing attachable to the photoinitiator by way, for example, of areaction of the photoinitiator with an unsaturated carboxylic acid. Anexample of an unsaturated carboxylic acid is acrylic acid or methacrylicacid. Particularly suitable in the context of the present invention arethe reaction products of Irgacure® 2959 with acrylic acid or methacrylicacid.

It is possible, accordingly, to use as component C a compound which hasboth a photoinitiator and a functional group polymerizable byirradiation with UV light or with electron beams or a functional groupcapable of reacting with at least one compound having an acidic hydrogenatom, or both.

The adhesive of the invention comprises component C in an amount of upto about 25% by weight, based on the total adhesive; the lower limitshould be situated at approximately 0.01% by weight. Based on theindividual photoinitiator molecule itself, irrespective of whether it iscovalently bonded to another compound, the portion in the adhesiveshould be situated at at least about 0.01% by weight up to about 10% byweight, preference being given to a proportion of from about 0.5 toabout 5% by weight, and with particular preference from about 1 to about3% by weight, based on the total adhesive.

In one preferred embodiment the adhesive of the invention may furthercomprise, as monofunctional reactive diluent, at least one compoundwhich possesses only one functional group polymerizable by irradiationwith UV light or with electron beams and which otherwise has no othergroups which are reactive in the sense of components A, B or C.Particularly suitable for this purpose are those compounds which areflowable at room temperature, especially corresponding esters of acrylicacid or methacrylic acid. Particularly suitable compounds are, forexample, the acrylic or methacrylic esters of aromatic or aliphatic,linear or branched C₄₋₂₀ monoalcohols or of corresponding etheralcohols, examples being n-butyl acrylate, 2-ethylhexyl acrylate,3-methoxybutyl acrylate, 2-phenoxyethyl acrylate, benzyl acrylate or2-methoxypropyl acrylate.

The monofunctional reactive diluents in the adhesive constitute afraction of up to about 50% by weight, but preferably below that level;for example, about 40% by weight, 30% by weight or about 20% by weight.The use of smaller amounts is likewise possible; thus the adhesive ofthe invention may also contain only 10% by weight, or an amount of fromabout 0.5 to about 8% by weight, of monofunctional reactive diluent.

Following the conclusion of a first curing stage by irradiation with,for example, electron beams or UV rays (in conjunction with acorresponding photoinitiator as component C), the adhesive of theinvention may cure by the influence of atmospheric moisture until therequired ultimate strength is attained. If, however, rapid attainment ofa certain ultimate strength is required, i.e., a high curing rate, inorder for example to enable the bonded materials to be processed furtheras rapidly as possible, the curing rate based on curing by atmosphericmoisture may be too low. In such cases, a curing agent may be added ascomponent D to the adhesive prior to processing.

The invention therefore additionally provides an adhesive whichcomprises

-   (d) as component D a compound having at least two acidic hydrogen    atoms.

As component D it is preferred to use a compound having at least twofunctional groups having in each case at least one acidic hydrogen atom,or a mixture of two or more such compounds, which are able to react withthe corresponding functional group of component A. The correspondingfunctional groups of component A in the context of the present text areall functional groups present in component A which are not polymerizableby irradiation under the conditions of the invention, especiallyisocyanate groups.

The compounds which can be used as component D preferably have amolecular weight of up to 2500. Functional groups having at least oneacidic hydrogen atom which are reactive with the correspondingfunctional groups of component A are suitably, in particular, primary orsecondary amino groups, mercapto groups or OH groups. The compoundswhich can be used as component D may have amino groups, mercapto groupsor OH groups in each case exclusively or in a mixture.

The functionality of the compounds which can be used in component D isgenerally at least about two. Preferably component D includes a fractionof compounds of higher functionality, having for example a functionalityof three, four or more. The total (average) functionality of thecomponent D is, for example, approximately two (for example, if onlydifunctional compounds are used as component D), or more—for example,about 2.1, 2.2, 2.5, 2.7 or 3. If desired, component D may have an evenhigher functionality—for example, about four or more.

Component D preferably comprises a polyol which carries at least two OHgroups. Polyols suitable for use in component D are all those polyolsmentioned in the course of the present text, provided they comply withthe restricting criterion of the upper limit on the molecular weight.

Component D is generally used in an amount such that the ratio of groupsof component A which are reactive with component D to groups ofcomponent D that are reactive with corresponding functional groups ofcomponent A is from about 5:1 to about 1:1, in particular from about 2:1to about 1:1.

The adhesive of the invention preferably comprises as component D acompound having at least two OH groups.

The adhesive of the invention generally has a viscosity at 50° C. offrom about 1000 mPas to about 30,000 mPas (Brookfield CAP 200, 50° C.,cone 6, 50 rpm, measurement time 25 s). In preferred embodiments of theinvention the viscosity of the adhesive is chosen so that at typicalprocessing temperatures it has a viscosity of from about 1000 mPas toabout 4000 mPas (Brookfield CAP 200, 25-150° C., cone 6, 50 rpm,measurement time 25 s). Typical processing temperatures are, forexample, from about 25 to about 70° C. in the case of the production offlexible packaging films, from about 70 to about 80° C. in the case ofthe lamination of high-gloss films, and from about 80 to about 150° C.in the case of applications in the textile sector.

If desired, the adhesive of the invention may further compriseadditives, which may account for a fraction of up to about 49% by weightof the overall adhesive.

Additives which may be used in the context of the present inventioninclude, for example, plasticizers, stabilizers, antioxidants, colorantsor fillers.

Plasticizers used are, for example, plasticizers based on phthalic acid,especially dialkyl phthalates, preference as plasticizers being given tophthalic esters which have been esterified with a linear alcoholcontaining about 6 to about 12 carbon atoms. Particularly preferred inthis context is dioctyl phthalate.

Likewise suitable as plasticizers are benzoate plasticizers, examplesbeing sucrose benzoate, diethylene glycol dibenzoate and/or diethyleneglycol benzoate in which from about 50 to about 95% of all hydroxylgroups have been esterified, phosphate plasticizers, an example beingt-butylphenyl diphenyl phosphate, polyethylene glycols and theirderivatives, examples being diphenyl ethers of poly(ethylene glycol),liquid resin derivatives, an example being the methyl ester ofhydrogenated resin, animal and vegetable oils, examples being glycerolesters of fatty acids, and polymerization products thereof.

Stabilizers or antioxidants which can be used as additives in thecontext of the invention include phenols, high molecular weight (M_(n))sterically hindered phenols, polyfunctional phenols, sulfur-containingand phosphorus-containing phenols or amines. Examples of phenols whichcan be used as additives in the context of the invention arehydroquinone, hydroquinone monomethyl ether,2,3-di-tert-butylhydroquinone, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene; butylated hydroxytoluene(BHT), pentaerythritoltetrakis-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; n-octadecyl3,5-di-tert-butyl-4-hydroxyphenylpropionate;4,4-methylenebis(2,6-di-tert-butylphenol);4,4-thiobis(6-tert-butyl-o-cresol); 2,6-di-tert-butylphenol;6-(4-hydroxyphenoxy) -2,4-bis (n-octylthio) -1,3,5-triazine;di-n-octadecyl 3,5-di-tert-butyl-4-hydroxy-benzylphosphonates;2-(n-octylthio)ethyl 3,5-di-tert-butyl-4-hydroxybenzoate; and sorbitolhexa[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; and alsop-hydroxydiphenylamine or N,N′-diphenylenediamine or phenothiazine.

Further additives may be included in the adhesives of the invention inorder to vary certain properties. Such additives may, for example, becolorants such as titanium dioxide, fillers such as talc, clay and thelike. If appropriate, small amounts of thermoplastic polymers may bepresent in the adhesives of the invention, examples being ethylene-vinylacetate (EVA), ethylene-acrylic acid, ethylene-methacrylate andethylene-n-butyl acrylate copolymers, which may impart additionalflexibility, toughness and strength to the adhesive. It is likewisepossible to add certain hydrophilic polymers, examples being polyvinylalcohol, hydroxyethylcellulose, hydroxypropylcellulose, polyvinyl methylether, polyethylene oxide, polyvinylpyrrolidone, polyethyloxazolines orstarch or cellulose esters, especially the acetates with a degree ofsubstitution of less than 2.5, which increase, for example, thewettability of the adhesives.

The adhesive of the invention preferably comprises

-   -   from about 10% by weight to about 99.9% by weight of component        A,    -   from about 0.1% by weight to about 90% by weight of component B,    -   from about 0% by weight to about 10% by weight of component C,    -   from about 0% by weight to about 49% by weight of component D,        and    -   from about 0% by weight to about 49% by weight of additives,        the sum of said constituents being 100% by weight.

In a particularly preferred embodiment the adhesive of the inventionpreferably comprises, approximately,

-   -   from about 15% by weight to about 99% by weight of component A,    -   from about 1% by weight to about 85% by weight of component B,    -   from about 0% by weight to about 10% by weight of component C,    -   from about 0% by weight to about 49% by weight of component D,        and    -   from about 0% by weight to about 49% by weight of additives,        the sum of said constituents being 100% by weight.

The adhesives of the invention can be prepared by customary techniqueswhich are known to the worker skilled in the art of preparing polymericmixtures.

In the context of the present invention, the adhesive of the inventionis customarily prepared by mixing the components stated in each case.

In principle, the adhesive of the invention can be used in the adhesivebonding of a very wide variety of materials. The materials which may bebonded include, for example, wood, metal, glass, vegetable fibers,stone, paper, cellulose hydrate, plastics such as polystyrene,polyethylene, polypropylene, polyethylene terephthalate, polyvinylchloride, copolymers of vinyl chloride and vinylidene chloride,copolymers of vinyl acetate-olefins, polyamides, or metal foils, ofaluminum, lead or copper, for example.

In one preferred embodiment the adhesive of the invention is used in theproduction of composite materials.

The present invention therefore further provides a process for producingcomposite materials which comprises using an adhesive of the invention.In another preferred embodiment, the composite materials which can beproduced with the aid of the adhesive of the invention are filmcomposites obtainable by the part-area or full-area adhesive bonding offilms.

The application of the adhesive of the invention to the materials to bebonded, especially the films, can be carried out using machinerycommonly used for such purposes, such as conventional laminatingmachines. A particularly appropriate procedure is the application of theadhesive in the liquid state to a film which is to be bonded to form alaminate. Subsequently, the film thus coated with the adhesive istransferred into an irradiation zone in which the polymerizationreaction, i.e., the crosslinking of the individual components, isinitiated by exposure to ultraviolet radiation. The adhesive of theinvention develops adhesion—for example, contact adhesion, butpreferably pressure-sensitive adhesion—by virtue of the irradiation andthe associated crosslinking reaction of the individual componentspresent in the adhesive. Following the irradiation procedure, the firstfilm coated with the irradiated adhesive is laminated with at least onesecond film, with or without the application of pressure.

This procedure is particularly advantageous for the mutual adhesivebonding of two films which are impervious to a radiation which isrequired for initiation of polymerization.

The bonding and laminating procedure described may be repeated a numberof times, so that it is possible to produce laminates which consist ofmore than two bonded layers.

The invention therefore further provides a composite material producedby a process of the invention using an adhesive of the invention.

The adhesive of the invention can be applied by all suitable methods tothe surfaces that are to be bonded; for example, by spraying or knifecoating.

The invention is illustrated below by means of examples.

EXAMPLES

Implementation of the Measurements:

Polyester films (polyethylene terephthalate (PET), thickness 50 μm) werecut to a size of about 15×19 cm and the surface was subsequently cleanedwith methanol. The test adhesive was knife coated onto half of the film,on a coherent region. Subsequently, the adhesive was exposed using a UVlamp (Ultra Jet 100 from Köhler); the exposure time was one second.Directly following exposure, a second film was applied congruently andpressed on with a manual roller. The film composite obtained in this waywas cut into strips 3 cm in width, and the thickness of the compositewas measured. The film thickness of the adhesive was in all cases fromabout 30 to 100 μm. Following the storage times indicated below, thepeel values were then determined for the purpose of testing strength.The peel values were measured in accordance with DIN 53539 using a Zwickmodel 144501/00 testing machine. Measurement was carried out with a 10kN force transducer and with a 0.1 kN force transducer. The test speedwas 100 mm/min. The strengths determined in this way are reported in theindividual examples, in N/15 mm.

Example 1 (Comparative Example)

A polymer having an NCO number of 4.4% by weight (molecular weight(M_(n)) about 2000) was prepared from 32% by weight of a polyesterhaving a molecular weight of about 800, 33% by weight of a polypropyleneglycol having a molecular weight of about 1000, 9% by weight of apolypropylene glycol having a molecular weight of about 400, 24% byweight of TDI and about 5% by weight of MDI. The viscosity was about5200 mPas (Brookfield CAP 200, 70° C., cone 6, 50 rpm, measurement time25 s). 10% of the NCO groups were reacted with hydroxyethyl acrylate.The product obtainable in this way (component A) had an NCO number ofabout 4.0 and a viscosity of about 5700 mPas.

One part of the photoinitiator Irgacure® 651 was added to 100 parts ofcomponent A. This mixture was subsequently tested for adhesion.

The values measured were as follows:

after 30 min 0.03 N/15 mm after 7 days 9 N/15 mm after 14 days 10 N/15mm

Example 2 (In Accordance with the Invention)

Component A:

A polymer having an NCO number of 4.4% by weight (molecular weight(M_(n)) about 2000) was prepared from 32% by weight of a polyesterhaving a molecular weight of about 800, 33% by weight of a polypropyleneglycol having a molecular weight of about 1000, 9% by weight of apolypropylene glycol having a molecular weight of about 400, 24% byweight of TDI and about 5% by weight of MDI. The viscosity was about5200 mPas (Brookfield CAP 200, 70° C., cone 6, 50 rpm, measurement time25 s). 10% of the NCO groups were reacted with hydroxyethyl acrylate.The product obtainable in this way (component A) had an NCO number ofabout 4.0 and a viscosity of about 5700 mPas.

Component B: Polyethylene Glycol-200 Diacrylate

Photoinitiator: Irgacure® 369

5 parts of component B and 1 part of photoinitiator were mixed with 100parts of component A. This mixture was subsequently tested for adhesion.

The values measured were as follows:

after 30 min 0.3 N/15 mm after 7 days 7 N/15 mm after 14 days 8 N/15 mm

Example 3 (In Accordance with the Invention)

Component A:

To prepare the component A, a commercially available, moisture-curing,NCO-containing laminating adhesive (LIOFOL UR 7746, from Henkel,Düsseldorf (DE)) was reacted with hydroxyethyl acrylate such that 10% ofthe NCO groups reacted to give the corresponding urethane.

Component B: Polyethylene glycol-200 diacrylate

Photoinitiator:

423.74 g of Capa 305 (trifunctional polycaprolactone, OH number=188.3)were reacted with 391.5 g of 2,4-TDI (NCO number=12.3%). 107.7 g (0.1mol) of this prepolymer were admixed with 219.6 g (1.0 mol) of Irgacure®2959 and the mixture was reacted until the NCO number had fallen to 0%.

5 parts of component B and 5 parts of photoinitiator were mixed with 100parts of component A. The mixture was subsequently tested for adhesion.

The values measured were as follows:

after 30 min 0.4 N/15 mm after 7 days 5 N/15 mm after 14 days 7 N/15 mm

Example 4 (In Accordance with the Invention)

Component A:

To prepare the component A, a polymer having acrylate groups andterminal NCO groups was prepared first of all. For this purpose, 102 gof a polyester (OH number 134) prepared from adipic acid, isophthalicacid, 1,2-propylene glycol and diethylene glycol, 74.52 g of a polyester(OH number 9, acid number 6) prepared from adipic acid, isophthalicacid, ethylene glycol and diethylene glycol, 22.63 g of propylene glycol(OH number 105), 53.7 g of TDI, 18.59 g of MDI and 10.34 g of2-hydroxyethyl acrylate were reacted with one another.

Component B: Trimethylolpropane triacrylate (TMPTA)

Photoinitiator: 15.27 g of Irgacure 907 and 6.11 g of Lucirin TPO

Component A was mixed with the stated amount of photoinitiator.Subsequently, 100 parts by weight of the resulting mixture were mixedwith 5 parts by weight of component B. This mixture was subsequentlytested for adhesion.

The values measured were as follows:

after 60 min 2.9 N/15 mm after 7 days 3.3 N/15 mm

1. A flexible laminate comprising: a first substrate consisting ofplastic film; a second substrate selected from the group consisting ofplastic film and metal foil; and an irradiated adhesive compositionpositioned between the first and second substrate, the adhesivecomposition comprising components A, B and D, (a) component A being atleast one polymer having a molecular weight (M_(n)) of at least 800 thathas at least one functional group polymerizable by irradiation withultraviolet (UV) light or with electron beams and has at least onefunctional group selected from the group consisting of isocyanate groupsand epoxy groups; capable of reacting with a compound having at leastone acidic hydrogen atom, (b) component B being at least one compoundhaving a molecular weight (M_(n)) of from about 100 to about 8000 whichhas at least two functional groups polymerizable by irradiation with UVlight or with electron beams; and (c) component D being a compoundhaving at least two acidic hydrogen atoms, wherein component A,component B and component D are each a different compound.
 2. Theflexible laminate of claim 1 wherein in the adhesive composition the atleast one functional group polymerizable by irradiation with UV light orwith electron beams of component A comprises a group having anolefinically unsaturated double bond.
 3. The flexible laminate of claim2 wherein in the adhesive composition component B comprises at least twogroups having an olefinically unsaturated double bond as functionalgroups polymerizable by irradiation with UV light or with electronbeams.
 4. The flexible laminate of claim 1 wherein in the adhesivecomposition component B comprises at least two groups having anolefinically unsaturated double bond as the functional groupspolymerizable by irradiation with UV light or with electron beams. 5.The flexible laminate of claim 1 wherein in the adhesive compositioncomponent A is a polymer selected from the group consisting ofpolyacrylates, polyesters, polyethers, polycarbonates, polyacetals,polyurethanes, polyolefins, nitrile rubber, styrene/butadiene rubber,and combinations thereof.
 6. The flexible laminate of claim 1 wherein inthe adhesive composition component A comprises at least onepolyurethane.
 7. The flexible laminate of claim 1 wherein the adhesivecomposition possesses a viscosity at 70 □C of from 1000 mPas to 6000mPas.
 8. The flexible laminate of claim 1 which further comprises (c) ascomponent C at least one photoinitiator which is capable of initiatingthe polymerization of olefinically unsaturated double bonds on exposureto UV radiation.
 9. The flexible laminate of claim 8 wherein component Ccomprises at least one photoinitiator obtained by reacting apolyfunctional alcohol having two or more OH groups with a di- ortriisocyanate and a photoinitiator having at least twoisocyanate-reactive functional groups and which is capable of initiatingthe polymerization of olefinically unsaturated double bonds on exposureto UV radiation.
 10. The flexible laminate of claim 9 wherein componentC comprises a photoinitiator obtained by reacting an at least trihydricalcohol with caprolactone to give a polycaprolactone which carries atleast three OH groups and has a molecular weight of from about 300 toabout 900, and subsequently linking the polycaprolactone with1-[4-(2-hydroxyethoxy) phenyl]-2-hydroxy-2-methylpropan-1-one by meansof a compound which carries at least two isocyanate groups.
 11. Theflexible laminate of claim 1 wherein a compound having at least two OHgroups is present as component D.
 12. The flexible laminate of claim 1wherein in the adhesive composition component B is an ester of acrylicacid or methacrylic acid with a polyol selected from the groupconsisting of aromatic polyols, aliphatic polyols and cycloaliphaticpolyols, or an acrylate ester of polyether alcohols.
 13. A method forproducing flexible composite materials, the method comprising: applyingan adhesive composition to at least a portion of a first substrate, saidfirst substrate consisting of a plastic film, the adhesive compositioncomprising components A, B and D: (a) component A being at least onepolymer having a molecular weight (M_(n)) of at least 800 that has atleast one functional group polymerizable by irradiation with UV light orwith electron beams and has at least one functional group “selected fromthe group consisting of isocyanate groups and epoxy groups”; capable ofreacting with a compound having at least one acidic hydrogen atom; (b)component B being at least one compound having a molecular weight(M_(n)) of from about 100 to about 8000 which has at least twofunctional groups polymerizable by irradiation with UV light or withelectron beams; and (c) component D being a compound having at least twoacidic hydrogen atoms, wherein component A, component B and component Dare each different compounds; irradiating the applied adhesive with UVlight or electron beams; and, contacting the irradiated adhesive with asecond substrate consisting of metal foil.
 14. The method of claim 13wherein in the adhesive composition the at least one functional grouppolymerizable by irradiation with UV light or with electron beams ofcomponent A comprises a group having an olefinically unsaturated doublebond.
 15. The method of claim 14 wherein in the adhesive compositioncomponent B comprises at least two groups having an olefinicallyunsaturated double bond as functional groups polymerizable byirradiation with UV light or with electron beams.
 16. The method ofclaim 13 wherein in the adhesive composition component A comprises anisocyanate group as the functional group capable of reacting with acompound having at least one acidic hydrogen atom.
 17. The method ofclaim 13 wherein in the adhesive composition component A comprises agroup having an olefinically unsaturated bond as the at least onefunctional group polymerizable by irradiation with UV light or withelectron beams and an isocyanate group as the at least one functionalgroup capable of reacting with a compound having at least one acidichydrogen atom.
 18. The method of claim 13 wherein in the adhesivecomposition component B comprises at least two groups having anolefinically unsaturated double bond as the functional groupspolymerizable by irradiation with UV light or with electron beams. 19.The method of claim 13 wherein in the adhesive composition component Ais a polymer selected from the group consisting of polyacrylates,polyesters, polyethers, polycarbonates, polyacetals, polyurethanes,polyolefins, nitrile rubber, styrene/butadiene rubber, and combinationsthereof.
 20. The method of claim 13 wherein the adhesive compositionfurther comprises (c) as component C at least one photoinitiator whichis capable of initiating the polymerization of olefinically unsaturateddouble bonds on exposure to UV radiation.
 21. The method of claim 20wherein component C comprises at least one photoinitiator obtained byreacting a polyfunctional alcohol having two or more OH groups with adi- or triisocyanate and a photoinitiator having at least twoisocyanate-reactive functional groups and which is capable of initiatingthe polymerization of olefinically unsaturated double bonds on exposureto UV radiation.
 22. The method of claim 21 wherein component Ccomprises a photoinitiator obtained by reacting an at least trihydricalcohol with caprolactone to give a polycaprolactone which carries atleast three OH groups and has a molecular weight of from about 300 toabout 900, and subsequently linking the polycaprolactone with1-[4-(2-hydroxyethoxy) phenyl]-2-hydroxy-2-methylpropan-1-one by meansof a compound which carries at least two isocyanate groups.
 23. Themethod of claim 13 wherein a compound having at least two OH groups ispresent as component D.
 24. The method of claim 13 wherein in theadhesive composition component B is an ester of acrylic acid ormethacrylic acid with a polyol selected from the group consisting ofaromatic polyols, aliphatic polyols and cycloaliphatic polyols, or anacrylate ester of polyether alcohols.
 25. A flexible composite materialcomprising: an irradiated adhesive composition sandwiched between afirst substrate consisting of plastic film and a second substrateconsisting of metal foil, the adhesive composition comprising (a)component A being at least one polymer having a molecular weight (M_(n))of at least 800 that has at least one functional group polymerizable byirradiation with UV light or with electron beams and has at least onefunctional group “selected from the group consisting of isocyanategroups and epoxy groups”, capable of reacting with a compound having atleast one acidic hydrogen atom; (b) component B being at least onecompound having a molecular weight (M_(n)) of from about 100 to about8000 which has at least two functional groups polymerizable byirradiation with UV light or with electron beams; (c) component C beingat least one photoinitiator having a molecular weight of more than about200 and which is capable of initiating the polymerization ofolefinically unsaturated double bonds on exposure to UV radiation; and,(d) component D being a compound having at least two acidic hydrogenatoms, wherein component A, component B and component C and component Dare each a different compound.
 26. The flexible composite of claim 25wherein in the irradiated adhesive composition component B is an esterof acrylic acid or methacrylic acid with a polyol selected from thegroup consisting of aromatic polyols, aliphatic polyols andcycloaliphatic polyols, or an acrylate ester of polyether alcohols.